TThe pharmacology and molecular pharmacology of various gastrointestinal (GI) peptides are being investigated. One peptide receptor family was concentrated on during the year: those for bombesin- (Bn) related peptides. Bn-related peptides (GRP, NMB) interact primarily with three distinct receptors (GRP-R, NMB-R) and the orphan receptor, BRS-3 to mediate a number of effects in the GI tract and central nervous system (CNS). The BRS-3 receptor has received considerable attention because BRS-3 knockout mice develop obesity, altered metabolism and diabetes. Until recently there were no selective agonists or antagonist to allow assessment of the importance of BRS-3 in various physiological/pathophysiological conditions. Recently both a selective nonpeptide agonist, MK-5046 and antagonist, Bantag-2 were described however there is limited information on their pharmacology. We performed a detailed study comparing their pharmacology to that of a universal peptide agonist, D-Tyr6, B-Ala11, Phe13, Nle14 Bn (6-14)(peptide #1) in both natural cells possessing BRS-3 and other Bn receptors and BN-R-transfected cells. Our results show that MK-5046 and Bantag are a highly selective agonist, competitive antagonist respectively, however the nonpeptide MK-5046 differs form the peptide agonist in kinetics, affinity, potency, ability to fully activate all signaling cascades and its duration of action. These differences many lead to important differences in physiological/pathophysiological studies. In a recent study we examined the molecular basis for the unique ability of a synthetic ligand of bombesin (D-Tyr6, B-Ala11, Phe13, Nle14 Bn (6-14)(peptide #1)) to function as a universal, high affinity agonist at all human bombesin receptor subtypes. In this study using 101 mutant receptors were made and expressed in CHOP cells to assess receptor affinities. 22 amino acids were identified that contributes to this high affinity of which 4 were especially important. The chemical properties of each of these were investigated in detail and the particular properties of each amino contributing to the high affinity were investigated. These results are now being extending in detailed mutagenesis studies to determine molecular basis for the difference in nonselective of peptide #1 to the selective nonpeptide BRS-3 agonist MK-5046 and the peptide antagonist, Bantag-1. It is anticipated the definition of the difference may lead to design of more selective ligands. Other studies this year not completed yet are attempting to identify selective PACAP/VIP receptor ligands withProf D. H.Coy are as well as with Prof M.Leopoldo to define the basis of affinity of selective BN-R nonpeptide ligands that he has developed for use in Bn receptor mediated imaging and cytotoxicity of cancer cells